Cruise Performance Optimization of the Airbus A320 through Flap Morphing

摘要

In the era of increasing aviation traffic the conditions are right to promote design of ambitious concepts. At Fokker Aerostructures attention is drawn to smooth in-flight shape morphing to produce a structurally functional Variable Camber Trailing Edge Flap (VCTEF). The deployment mechanism would fit into the flap, not limiting other functionality such as Fowler motion, while at the same time allowing small camber variations during cruise. This is based on the assumption that such morphing will bring performance improvements which are commercially interesting. The main goal of this research was therefore to predict these performance benefits and thus the applicability for a specific case of the Airbus A320 aircraft in cruise flight. This aircraft is large enough to accommodate the technology, it is operated in great numbers and cruise is the most fuel demanding part of its mission. Since the concept is in the development phase the further task is to determine the morphing design setup which performs best. The amount of morphing is driven by a circular reference function, which is added to the base geometry at any desired streamwise cut of the wing by manipulation of the airfoil coordinates as seen on the cover. The design is specified by the points on the airfoil upper surface where the morphing begins and ends, boundaries of the morphing region where upper surface bending is allowed. As also found in other literature it is shown that morphing can bring drag reduction for a section, wing and the complete aircraft. This varies throughout the cruise, which is translated to more sophisticated performance indicators for comparison and evaluation of the benefits. The first indicator is the increase of range over the design mission for the given aircraft. The second and third are the fuel savings which can either be obtained by increasing the cruise end weight, or by decreasing the cruise beginning weight, both by the amount of the saved fuel while keeping the aircraft range constant. In order to evaluate these indicators, the Breguet range equation is used in a discretized form, utilizing an interpolated lift-to-drag ratio determined by aerodynamic analysis at 7 cruise points. This was done using both the 2D solverMSES and a quasi-3D tool Q3D developed at TU Delft comprising ofMSES and AVL vortex lattice solver. For the analysis a complete A320 model is required, which was not available and was created from the known performance data and partially assumed geometry. The unknown wing geometry was optimized with respect to the mid-cruise drag simulating an already efficient aircraft, as suggested by literature. Other model components were the horizontal stabilizer, fuselage and center of gravity position allowing trim at the reference cruise points and obtaining the lift requirements for the wing and a representative section. Under these lift requirements the 2D and 3D analyses were performed at individual cruise points to obtained improved lift-to-drag ratios which could be then used to evaluate the range improvement. Itwas found thatwith morphing in 2Dthe drag reduction can amount up to 9% at the beginning of cruise but parabolically decreases towards mid cruise after which it remains below 0.5%. This is primarily due to manipulation of the shockwave and the boundary layer at the given lift requirements, which is most dominant at high cruise lift coefficients. Since the induced drag was found not affected by the assumed morphing, such improvements are further scaled down when evaluated for the entire wing and even further from the aircraft point of view, resulting in a range improvement in order of 20km and fuel savings of below 0.5% of trip fuel. A sensitivity analysis on the design variables has shown that these performance benefits have small sensitivity to the size of the morphing region and that a very aft located regions are the most beneficial, suggesting that a small tab at the trailing edge might be a better and easier solution. In view of these results the smooth morphing concept is deemed not applicable for the cruise of short range aircraft such as A320. However, given the parabolic behaviour of the drag improvements, larger potential can be expected for long range aircraft, which is the main resulting recommendation of the conducted research. Furthermore it cannot be excluded that other regimes could benefit more from the morphing concept, such as high-lift, which would probably require wind-tunnel testing, as discussed in the final Appendix of this work.